Crustal Thickness Research Articles

On the equilibrium limit of liquid stability in pressurized aqueous systems

Phase stability, and the limits thereof, are a central concern of materials thermodynamics. However, the temperature limits of equilibrium liquid stability in chemical systems have only been widely characterized under constant (typically atmospheric) pressure conditions, whereunder these limits are represented by the eutectic. At higher pressures, the eutectic will shift in both temperature and chemical composition, opening a wide thermodynamic parameter space over which the absolute limit of liquid stability, i.e., the limit under arbitrary values of the thermodynamic forces at play (here pressure and concentration), might exist. In this work, we use isochoric freezing and melting to measure this absolute limit for the first time in several binary aqueous brines, and nodding to the etymology of “eutectic”, we name it the “cenotectic” (from Greek “κοινός-τῆξῐς”, meaning “universal-melt”). We discuss the implications of our findings on ocean worlds within our solar system and cold ocean exoplanets; estimate thermodynamic limits on ice crust thickness and final ocean depth (of the cenotectic or “endgame” ocean) using measured cenotectic pressures; and finally provide a generalized thermodynamic perspective on (and definition for) this fundamental thermodynamic invariant point.

Quantifying Crustal Growth in Arc‐Backarc Systems: Gravity Inversion Modeling of the Lau Basin

AbstractThe formation and evolution of arc‐backarc systems govern crustal production in some of the most volcanically and hydrothermally active environments on Earth. This study presents the first complete three‐dimensional density model of the active arc‐backarc system in the southwest Pacific comprising the Lau Basin and Tofua arc. Seafloor density and crustal thickness maps reveal changes in crustal composition and growth rates throughout the basin and along the volcanic arc. Crustal thickness varies significantly between the different centers of accretion (i.e., assemblages), resulting from seafloor spreading and subsurface melt accumulation below volcanic fields. Volumetric growth rates were calculated for each assemblage, corresponding to their respective contribution to basin expansion. The highest crustal density and growth rates are thought to be related to a mantle‐derived melt source entering the basin from the north around the edge of the subducting Pacific Plate. This study shows that the inverse modeling approach can be applied to global gravity data sets to characterize and quantify the density and thickness of the crust anywhere in the oceans.

Insight into intracontinental deformation and crustal reworking of ancient continents implied by crustal structure imaging of the Yangtze Craton

The crustal imprints from multistage tectonic activities in cratons offer valuable insights into continental evolution. Utilizing seismic data from two densely deployed, nearly perpendicular linear arrays, and a newly developed stepwise joint inversion of depth-domain receiver function and surface wave dispersion, we constructed a detailed crustal layering model for the Yangtze Craton. Our analysis revealed elongated double velocity reversal zones as salient features of the crust, which likely record ancient crustal reworking and juvenile crustal growth associated with Neoproterozoic rift-related magmatic processes. The interlayering of low- and high-velocity structures may contribute to the enduring stability of the Yangtze Craton. Additionally, superimposed layers separated by east-dipping interfaces and abrupt changes in crustal thickness in the boundary belts surrounding the Yangtze Craton document the crust's structural responses to intracontinental deformation during continent assembly.

The viscosity of a partially molten layer in a paleo-orogenic plateau

Orogenic plateaus (e.g., Tibet, Altiplano) are characterized by broad, flat-top topography at high elevation and significantly increased crustal thickness. Partial melt is thought to weaken the middle crust of orogenic plateaus, and thus reduce the viscosity of the crust; however, the amount of partial melt and the magnitude of associated weakening remain unconstrained. The New England Appalachians represent an exposed mid- to lower crustal section of a paleo-orogenic plateau, similar to modern-day Tibet. In this study, we utilize the relationship between the spacing of deformation bands and the compaction length to constrain mid-crustal shear viscosity in a late Devonian migmatite. We find that the viscosity of the middle orogenic crust in the paleo-orogenic plateau of the New England Appalachians is 1017–18 Pa∙s at ∼3–9% melt. This finding is consistent with geophysical models of orogenic channel flow and provides field-based evidence for a significant rheologic transition at low melt-fraction. Our results suggest that the key elements for the formation of a weak, mid-crustal layer in orogenic plateaus are an influx of water and temperatures near the hydrous granite solidus.

Interaction of Kerguelen and Amsterdam-St. Paul dual hotspots with Southeast Indian Ridge

We investigated the influence of the Kerguelen (K) and Amsterdam-St. Paul (ASP) dual hotspots on mantle evolution and crustal accretion in the eastern Indian Ocean. Using surface plate motion constraints from the global plate reconstruction model and the 3-D mantle convection code (ASPECT), we illustrated detailed processes of mantle upwelling, melting, and crustal accretion in the ridge-dual hotspot system. Model results demonstrate that the K hotspot significantly increased the mantle temperature over a wide region of over 1,500 km, leading to a 1–2 km increase in average crustal thickness along the entire Southeast Indian Ridge (SEIR). Only ridge-dual hotspot interaction models can explain key crustal variations along the SEIR. Gravity analysis revealed the K hotspot's long-term interaction with nearby ridges formed significant crustal anomalies, while the ASP hotspot's 10 Myr interaction with SEIR created localized anomalies. The distance between the ridge and hotspot, as well as plume flux, are key factors controlling the strength of ridge-hotspot interaction. The K hotspot, with its relatively higher plume flux, has double the influence distance of the ASP hotspot. Furthermore, our models indicate a possible direct interaction between the K and ASP hotspots, resulting in the ASP plume materials flowing towards the K plume.

Norwegian scabies in HIV and tuberculosis infected patient: A case report

Norwegian scabies is a rare scabies with the manifestation of thick crusts of the extremities of the skin that contain eggs and mites. Several conditions in which scabies infection is easily transmitted include immunocompromised, home nursing, and severe neurological disorder. The aim of this case report was to present a thorough analysis of a comprehensive resource for the management of Norwegian scabies patients, with a specific focus on individuals who also have HIV or other immunocompromising diseases. A 56 – year – old female presented with dermatitis lesions and itching with sever hyperkeratosis, several maculae and papules on neck and armpits for four months duration.Sarcoptes scabiei was found from microscopy examination of skin scraping. The patient received antiretroviral drugs, antituberculosis medication and scabicidal treatment.

Fine-scale Southern California Moho structure uncovered with distributed acoustic sensing.

Moho topography yields insights into the evolution of the lithosphere and the strength of the lower crust. The Moho reflected phase (PmP) samples this key boundary and may be used in concert with the first arriving P phase to infer crustal thickness. The densely sampled station coverage of distributed acoustic sensing arrays allows for the observation of PmP at fine-scale intervals over many kilometers with individual events. We use PmP recorded by a 100-km-long fiber that traverses a path between Ridgecrest, CA and Barstow, CA to explore Moho variability in Southern California. With hundreds of well-recorded events, we verify that PmP is observable and develop a technique to identify and pick P-PmP differential times with high confidence. We use these observations to constrain Moho depth throughout Southern California, and we find that short-wavelength variability in crustal thickness is abundant, with sharp changes across the Garlock Fault and Coso Volcanic Field.

Subduction Style at Different Stages of Geological History of the Earth: Results of Numerical Petrological-Thermomechanical 2D Modeling

In this article we examine the effects of impact of slab rocks eclogitization on the subduction regime under the continent. Eclogitization of rocks in high-pressure metamorphic complexes occurs only in the areas of penetration of hydrous fluid. In the absence of hydrous fluid, the kinetic delay of eclogitization preserves low-density rocks under P‒T conditions of eclogite metamorphism, delaying the weighting of a slab and reducing the efficiency of the slab-pull mechanism which contributes to the steep subduction into the deep mantle. The results of numerical petrological-thermomechanical 2D modeling of subduction under the continent in a wide range of eclogitization parameters of oceanic crust rocks (discrete eclogitization) are presented. The effects of a lower kinetic delay of eclogitization in the water-bearing basalt layer, compared to the drier underlying gabbro layer, have been tested. Based on results of 112 numerical experiments with 7 variants of eclogitization ranges (in range 400–650°C for basalt and 400–1000°C for gabbro) at different potential mantle temperatures (ΔT = 0–250°C, above modern value), and steep, flat and transitional subduction regimes were identified. The mode of steep subduction occurs under modern conditions (ΔT = 0°C) with all ranges of eclogitization. Here it is characterised by an increase in the angle of subduction of the slab as the plate descends, and above the boundary of the mantle transition zone there is a flattening or and then tucking of the slab. Subduction is accompanied by the formation of felsic and mafic volcanics and their plutonic analogues. At elevated temperatures of the mantle (ΔT≥150°С) and discrete eclogitization over a wide range, the flat subduction regime is observed with periodic detachments of its steeper frontal eclogitized part. The flat subduction regime is accompanied by significant serpentinization of the mantle wedge and episodic, scarce magmatism (from mafic to felsic), which occurs at a significant distance (≥500 km) from the trench. During the transition regime, which is also realised in models with elevated mantle temperatures, there is a characteristic change occurs from flat to steep subduction, resulting in a stepped shape of the slab. As the kinetic shift of eclogitisation increases, flat subduction develops. An increase in the thickness of the continental lithosphere from 80 km to 150 km contributes to the implementation of steep subduction, while the influence of the convergence rate (5–10 cm/year) is ambiguous. Discrete eclogitization of thickened oceanic crust and depletion of lithospheric mantle in the oceanic plate are the main drivers of flat subduction. In modern conditions, their influence becomes insignificant due to the decrease in the thickness of the oceanic crust and the degree of depletion of the oceanic mantle lithosphere. As a result, the less frequent flat movement of slabs is determined by other factors.

The Petrogenesis of Devonian Volcanism and Its Tectonic Significance in the Kalatag Area, Eastern Tianshan, Xinjiang, China

The Kalatag mineralization belt is an important metallogenic belt of polymetallic mineral deposits in the northern part of eastern Tianshan, and its age and tectonic setting are still controversial. We identified a set of Devonian volcanic rocks hosted in the Early Palaeozoic package of dominantly marine sediments with a small amount of terrestrial rocks. This study presents petrological, U–Pb geochronology, and geochemical data for the volcanic rocks. The ages of the rhyolite (407.2 ± 1.9 Ma) and basaltic andesite (380.4 ± 2.8 Ma) suggests that the Kalatag belt is a Devonian volcanic succession. These rocks consist mainly of marine calc–alkaline lava, tuff, pyroclastic rocks, and minor terrestrial basaltic andesite. The lavas are characterized by the enrichment of light rare earth elements and strongly depleted in Nb and Ta, typical of island arc magmatic rocks. The volcanic rocks probably originated from the partial melting of the mafic lower crust which was modified by subducted slab-related fluids. During their ascent through the crust, these volcanic rocks underwent variable extents of fractional crystallization (rhyolites) and crustal contamination (basaltic andesites). Combined with the results of previous studies, we suggest that the Devonian rocks formed in an island arc related to the northward subduction of the Northern Tianshan Ocean with a crustal thickness of ~35–40 km.

Far-field response to the closure of the Meso-Tethys Ocean: New geochronological evidence from the Chem Co graben in the westernmost part of Central Tibet

The Chem Co graben is located in the westernmost part of the Qiangtang block, central Tibet. It is adjacent to the Longmu Co Fault to the north and approximately 50 km away from the Karakoram Fault to the west. The formation of the graben resulted in the exposure of basement rocks in the footwalls of the graben bounding normal fault, which hold crucial information on the Mesozoic closure of the Meso-Tethys Ocean. Garnet-biotite schist crops out sporadically in the footwall of the graben-boundary normal fault, and is intruded by leucogranite dikes. Pseudosection modeling indicates peak metamorphic conditions for the schist of 590–670 °C and 4.5–7.5 kbar, similar to the conditions of mid-crustal rocks at the western end of the Qiangtang block. Field investigations and microstructural analysis suggest syn-kinematical left-lateral strike-slip in both the biotite schist and granitoid veins. Zircon U − Pb, monazite U − Th − Pb, and 40Ar/39Ar ages show that intense regional intensive tectonic deformation and contemporaneous magmatism began at ∼120.6 Ma and ended with the peak metamorphism conditions at 105.3 ± 6.0 Ma. These results indicate that the closure of the Meso-Tethys Ocean in the westernmost part of central Tibet occurred over this period (i.e., 121–105 Ma) with final closure during the late Early Cretaceous. The closure of the Meso-Tethys Ocean likely triggered widespread far-field responses, extending from the Altyn Tagh Fault to the Longmu Co Fault, and reaching the Pangong and Hunza regions around the Western Himalayan Syntaxes. Episodic crustal thickening and surface uplift since the closure of the Meso-Tethys Ocean caused the upper crust to be extruded along the westernmost part of central Tibet, leading to the formation of the Chem Co graben.

Microscopic description of the pygmy and giant dipole resonances in even–even nuclei. Application to the isotopes 150,152,154,156,158,160Gd

This paper deals with a microscopic approach for the description of the pygmy dipole resonance (PDR) as well as of the giant dipole resonance (GDR). The formalism is based on a Hamiltonian which is summing a mean field term, the pairing for alike nucleons and the dipole–dipole interaction. Two features are specific for our description: (a) The use of a projected spherical single particle basis and (b) the involved dipole operator is a Schif-like operator including a corrective term which is cubic in the radial coordinate. The dipole strength distribution with energy is plotted for the PDR region, i.e., [0,10] MeV. The dominant transitions have an isovector character for three isotopes and isoscalar for another three. The PDR states carry only 0.4–1.8[Formula: see text] of the total EWSR. The dependence of the dipole strength on nuclear deformation is evidenced. For the whole interval of [0,20] MeV the dipole strength was first folded by Lorentzian of 1[Formula: see text]MeV width and then plotted as function of the QRPA energies. The peaks belonging to each of the two ranges are analyzed in detail and their nature, isovector/isoscalar, was pointed out. The r-cubic term and the nuclear deformation have opposite effects on the dipole strength. The famous Thomas–Reiche–Kuhn sum rule formula is generalized to the case of the Schiff dipole momentum. The new EWSR is very well satisfied. The photoabsorbtion cross-section is calculated and compared with experimental data in a figure showing its dependence on energy. The total cross-section, [Formula: see text], the moments of the integrated cross-sections, [Formula: see text], [Formula: see text], the dipole polarizability and the thickness of the neutron crust are also calculated. The main features of PDR and GDR are realistically described.

On the relationship between the uppermost mantle (≤220 km) seismic velocity, crustal thickness, and topography in Tibet

We propose that the mantle lithospheric density and crustal thickness are correlated in such a way as to produce a flat Tibetan Plateau. We observe that the mantle lithosphere is relatively uniform beneath the Himalaya and southern and central Tibet, despite a near doubling of crustal thickness relative to India. Farther north, cratonic mantle lithosphere disappears over large regions of north-central Tibet, giving rise to large lateral variations in uppermost mantle Vs anomalies (>12%) that are uncorrelated with changes in surface elevation but are closely related to changes in crustal thickness. This decoupling of surface topography from spatial variations in upper mantle seismic velocity, and assumed buoyancy, implies that Tibetan topography is controlled by a crust-mantle interaction that is able to maintain its near constant elevation. This crust-mantle interaction is likely driven by gravitational potential energy with a very weak crust. Magmatism, with ages of ca. 20 Ma to Present, spatially correlated with this region with no sub-Moho mantle lithosphere implies destabilization of mantle lithosphere in northern Tibet. Cratonic Indian underthrusting for the past 25 m.y. has also not led to significant topography in the plateau through time. The magmatism may have helped weaken the crust, allowing it to respond to changes in uppermost mantle buoyancy, resulting in a flat plateau.

Late Cretaceous glaciations in a hyper-arid plateau desert of the South China Coastal Mountains

Increasing evidence indicates the existence of a cryosphere during the Cretaceous supergreenhouse. However, current understanding of a potential link between lithosphere dynamics and cryospheric processes in the Cretaceous plateau desert successions of China remains limited. We report the occurrence of ice-rafted dropstones and diamictites from the Upper Cretaceous Chishan Formation of the Subei Basin at the East Asian continental margin. Our provenance results indicate that fluvial deposits of the Lower Chishan Formation were mainly derived from the Sulu Orogen to the north and the Zhangbaling Uplift to the west, whereas aeolian deposits of the Upper Chishan Formation were largely recycled from the two sources with an additionally notable contribution from the post-Cretaceous basement of the Yangtze Block. Combined with previous evidence, provenance analysis indicates that Late Cretaceous collision between the Okhotomorsk Block and the East Asian continent led to the growth of the South China Coastal Mountains via crustal thickening, which generated an arid, high-altitude basin region that experienced desertification and paleohydrological variability, and that was supplied with additional clastic sediment sources from the basement of the South China Block. Our results provide evidence of Late Cretaceous cryospheric processes in a continental mid-latitude plateau desert linked to the northwestward subduction and collision of the paleo-Pacific realm. Global cooling from the late Turonian to Maastrichtian drove the establishment of glaciers in high-altitude mountains leading to the development of ice-related deposits in the plateau deserts, as recorded in the Subei desert basin of the South China Coastal Mountains. The record of ice-rafted debris and the provenance signature reveal an active Cretaceous plateau cryosphere linked to lithosphere dynamics.

Reduction of oil absorption and acrylamide content in banana slices by infrared frying

AbstractBackgroundThe crust characteristics of fried crisps determine their oil absorption. Starch structures, as the main components of fried starchy fruits and vegetables, influence their crust formation and properties. This study investigated the reduction of oil uptake and acrylamide content in infrared‐fried (IF) banana slices by modifying starch structures at varying infrared power levels.ResultsInfrared heating improved heat transfer and surface moisture removal in fried banana slices. It facilitated crust formation in the IF samples and produced increased crust uniformity, crust ratio, and hardness. Analysis of the porous properties showed that the volume fraction of pores sized 100–250 μm was reduced in IF samples but the proportion of pores with a diameter ranging from 0.02 to 10 μm was increased. Infrared frying reduced the total oil uptake, surface oil, and structural oil content in banana slices, and each of these measures decreased as infrared power levels increased. Characterization of the starch structures suggested that the damage to the crystalline structure was increased in IF samples and more starch‐lipid complexes were generated, which would be responsible for the formation of a denser and thicker crust. The acrylamide content in the IF sample was reduced, as determined by liquid chromatography–tandem mass spectrometry (LC–MS/MS).ConclusionModifications to starch structures (crystalline structures and chemical structures) play a crucial role in oil absorption in fried starchy fruits and vegetables. Infrared frying can be used as an alternative method to produce low‐fat fruits and vegetable crisps with reduced acrylamide content. © 2024 Society of Chemical Industry.

Modelling the evolution of an ice sheet’s weathering crust

Abstract The weathering crust is a layer of porous ice that can form at the surface of an ice sheet. It grows and decays in response changing weather and climate conditions, affecting the albedo, the melt rate, and the transport of meltwater across the surface. To understand this behaviour, we seek time-dependent solutions to a continuum, thermodynamic model for the porosity, temperature and thickness of the weathering crust, and the internal and surface melt rates. We find solutions using a numerical enthalpy method, presented in this study. We use idealised ‘switching’ and sinusoidal forcings to explore the different dynamics exhibited during growth and decay, the timescales involved, and the impact of diurnal vs. annual variations. The results demonstrate qualitative agreement with observations, and provide insight into the relative importance of different surface heat fluxes during the growth and decay of the crust. The model therefore provides a useful tool for exploring the response of the weathering crust to climate change.

Lunar Nearside‐Farside Mare Basalt Asymmetry: The Combined Role of Global Crustal Thickness Variations and South Pole‐Aitken (SPA) Basin‐Induced Lithospheric Thickening

AbstractLunar mare basalts represent melting of mantle material, buoyant ascent in dikes, and eruption onto <20% of the surface. Global mare distribution is distinctly asymmetrical, with a paucity on the farside, plausibly interpreted to be related to thicker farside low‐density crust inhibiting buoyant magma rise to the surface. Challenging this hypothesis is the presence of the huge, ancient farside South Pole‐Aitken (SPA) basin, site of the thinnest crust and deepest depression observed on the Moon. We hypothesize that an oblique impact stripped the farside crust within the SPA basin, permitting early mare basalt emplacement as cryptomaria due to thin/absent crust. However, removal of the SPA thermally insulating megaregolith/crust accelerated lithosphere thickening beneath the basin. This deepening rheological barrier inhibited buoyant rise of mantle diapirs below SPA, resulting in early abatement of mare basalt extrusions compared to the nearside, and retention of the deep, underfilled SPA impact basin observed today.

Relaxation States of Large Impact Basins on Mercury Based on MESSENGER Data

AbstractThe crustal structure of Mercury's large impact basins provides valuable insights into the planet's geological history. For a warm crust, a post‐impact basin structure will viscously relax with inward flow of crustal materials toward the basin center. This effect drastically diminishes the crustal thickness contrasts and associated Bouguer gravity contrasts between the basin center and its surroundings. Here, we analyze Bouguer contrasts of 36 basins (diameter 300 km) located in the northern hemisphere as a proxy for viscoelastic relaxation. Thermal evolution models, assuming the present 3:2 spin‐orbit configuration, are used to predict crustal temperatures. Our analysis reveals that the expected correlation between zones of warm crust and low Bouguer contrast from relaxation is not observed in the available data. This suggests that crustal temperatures have changed in the past, potentially due to a change in Mercury's orbit or to a major volcanic event associated with smooth plain formation.

Iron isotope fractionation during transcrustal magmatic differentiation: Implications for continental crustal formation in subduction zones

Earth’s continental crust is hypothesized to originate from mantle melting in subduction zones. However, mantle melts are typically Fe-rich, with light Fe isotopes (δ56Fe = 0.05‰), unlike the Fe-depleted and heavy Fe isotope (δ56Fe can be up to 0.2‰) compositions of continental crust. The mechanisms responsible for this paradox remain elusive. Here, we report Fe isotope data from a suite of co-magmatic Middle Triassic continental arc rocks in the Ailaoshan tectonic zone (Yunnan, SW China). Gabbroic diorites have light Fe isotopes (δ56Fe = 0.04‰−0.09‰), while granodiorites and normal-arc granites have slightly heavier values (δ56Fe = 0.07‰−0.14‰). Adakitic granites, with high Sr/Y (61−183) and La/Yb (47−90) ratios, exhibit the heaviest δ56Fe (0.16‰−0.19‰). Rayleigh fractionation modeling results suggest that fractionation of isotopically light Fe minerals (e.g., olivine, pyroxene, and amphibole) can reproduce the Fe isotopic variations in most samples, but fails to explain the high Sr/Y, La/Yb, and δ56Fe values of adakitic granites, which would require Fe-rich garnet fractionation. Notably, the different Fe isotopes of the adakitic granites and non-adakitic rocks reveal two distinct transcrustal magmatic differentiation pathways: lower crustal, high-pressure, garnet-dominated fractionation; and middle−upper crustal, amphibole-dominated fractionation. The heavy Fe isotopic and Fe-depleted characteristics of the Ailaoshan magmatic arc suites are more comparable to the calc-alkaline arc magmas from normal to thick crust arcs (e.g., the Andean arc), but remarkably different from the tholeiitic arc magmas from thin crust arcs (e.g., the Mariana arc). This study highlights the role of amphibole and garnet fractionation in magmatic calc-alkaline differentiation. We propose that a thickened crust would permit a longer magmatic differentiation column, thus facilitating felsic and Fe-depleted continental crustal formation. The fractionated Fe-rich, garnet-bearing arc cumulates with light Fe isotopes are density-unstable and may be recycled into the mantle by lower crustal foundering.

THE EVOLUTION OF A CLAY CRUST IN A BOREHOLE

Based on the previously proposed quasi-stationary model of clay crust formation when drilling wells in depth intervals with permeable rocks, software was created and computational experiments were performed, which made it possible to clarify the contribution of various physical parameters to the process of its growth.Based on the analysis of the results of computational experiments, the contribution of the physical parameters of the formation and clay crust to the dependence of its size on time has been clarified. The model assumes that the filtration pressure fields are described by stationary piezo conductivity equations. This made it possible to construct explicit dependences of pressure, thickness of the clay crust, radius of the zone of pressure disturbances in the reservoir during drilling and other parameters on time. Simple approximate formulas have been found for the dependence of the thickness of the clay crust, the filtration rate and the radius of the pressure disturbance zone in the reservoir on time, which describe their evolution with high accuracy.Based on the analysis of the calculation results, it was found that the thickness of the clay crust significantly depends on the permeability of the reservoir and repression, and these parameters determine the process of its formation. The porosity of the collector makes a smaller contribution, and the filtration and capacitance parameters of the clay crust have little effect on its thickness.New possibilities for estimating the physical parameters of reservoirs based on cavernometry have been identified. The solution of this problem is especially important for horizontal wells, in which the clay crust intervals have a significant length, and its formation occurs under conditions of a wide range of reservoir properties of the formation. The considered problem is of practical importance, since the zone of penetration of drilling mud filtrate into the formation has a screening effect on the use of geophysical methods to determine reservoir saturation. The results obtained can be used both to improve the interpretation of geophysical methods and to develop those.When conducting computational experiments using an exact formula, the stochastic behavior of the calculated curves was found. It was found that the noted effect is associated with rounding error, and in this sense is a manifestation of the features of the processor. An approach is proposed to eliminate the detected stochastic errors.

Protracted magma evolution and transcrustal magmatic plumbing system architecture at Erta Ale volcano (Afar, Ethiopia)

Abstract The Afar region is one of the only places on Earth where magmatic continental rifting and associated ongoing break-up processes are exposed onshore. The several active magmatic segments there are characterized by contrasted morphologies, crustal thicknesses, magma production rates, and magma-tectonic styles. In the Erta Ale Range rift segment, extension is magmatically accommodated, making the range the ideal place to study the magmatic behavior of a mature rift segment. Erta Ale Range comprises sub-segments with magma compositions ranging from basalts to rhyolites, but only the Erta Ale Volcano (EAV) sub-segment is active, where only basaltic compositions have been reported so far. Here, we show for the first time protracted differentiation at EAV that is not expressed volcanically at the surface, but is rather accessible via unique cognate gabbroic and microgabbroic blocks, and recorded by mixing with erupted basaltic magmas. These cognate samples record previously unknown mushy and evolved parts of the EAV plumbing system. To constrain their origin and evolution, we measured the major and trace element compositions of the bulk rocks, interstitial glasses, and melt inclusions. We also measured the oxygen isotopic compositions of olivine crystals, interstitial glasses, and melt inclusions. By combining these results with textural relationships and oxy-thermo-barometry calculations, we discuss magma differentiation and storage conditions, as well as magmatic interactions during transport through the crust. Comparison of our results with rhyolite-MELTS thermodynamic models highlights that protracted fractional crystallization is the main process of magma evolution, and when associated with reactive porous flow is capable of forming the evolved compositions observed (up to 75 wt.% SiO2). We also use the model outputs to quantify distinct steps of igneous differentiation in both shallow and deep crustal reservoirs, and we highlight significant interactions with hydrothermally altered wall rocks. We discuss this model within the geological contexts of the Erta Ale Range rift segment and the larger Afar region, and highlight contrasts with mature oceanic systems to argue that the region is not in the final stages of continental break-up.